The invention lies in the printing technology field. More specifically, the invention relates to a dampening unit of a planographic printing machine, with a pan roller, a transfer roller, and a dampening unit roller. The transfer roller is held against the dampening unit roller with a regulating force, generated by a weight, gas-pressure, or a spring force (FF). The various rollers, in particular, are ink-friendly and therefore emulsion-carrying rollers.
U.S. Pat. No. 4,290,360 (German patent DE 29 02 228 C2) describes two different embodiments of a dampening unit. In the dampening unit of the first exemplary embodiment described therein (see FIG. 1 of the patent), which corresponds to the generic type mentioned above, a dampening unit roller bears against an applicator roller under the action of a spring, but the dampening unit roller is not pivotable about a pivot axis offset relative to the roller axis of a water pan roller. The water pan roller itself is not pivotable at all. Also, the pivot axis of the dampening unit roller which is coaxial with the water pan roller, does not lie essentially on a tangential line running through a circumferential contact point which is formed by the dampening unit roller together with the applicator roller. Instead, it is far removed from the tangential line. In the second exemplary embodiment described in the patent (see FIG. 5 of the patent) the dampening unit is different from the above-mentioned generic type. A dampening unit roller is mounted, together with a water pan roller, in a carrier and it is pivotable about a pivot axis that is offset relative to the roller axis of the water pan roller and is formed by a journal. Although a spring acting on the carrier ensures that the applicator roller remains in bearing contact against a plate cylinder, the dampening unit roller is not held against the applicator roller under the action of a spring force. Those two dampening units are not so-called emulsion film dampening units or alcohol-free direct film dampening units.
A further dampening unit is described in German published patent application DE 29 09 765. The transfer roller is pivotable about the roller axis of a water pan roller. It is not pivotable about a pivot axis that is offset relative to the roller axis.
A further dampening unit is described in German published patent application DE 28 22 350 A1. There, although a metering roller carried in arms is pivotable about a pivot axis offset relative to the roller axis of a pan roller, the metering roller is not held in bearing contact against a dampening unit roller under the action of a regulating force, such as, for example, a weight, gas-pressure or spring force. Moreover, the pan roller is not pivotable about the offset pivot axis. That prior art dampening unit, furthermore, is not a so-called emulsion film dampening unit, because not all the dampening unit rollers arranged in the transport path of the dampening medium are ink-friendly and, for example, rubberized. For the reasons mentioned above, the dampening unit described contradicts the principle of alcohol-free or reduced emulsion film dampening.
U.S. Pat. No. 4,949,637 describes a further dampening unit, in which each dampening unit roller guides both printing ink and dampening medium and, for this purpose, consists of rubber. The roller is driven at a circumferential speed that corresponds to the circumferential speed of the plate cylinder. Such dampening units are conventionally also designated as alcohol-free or reduced direct film dampening units or emulsion film dampening units. The dampening unit comprises a transfer roller which is mounted in a pivotable supporting element and which is pivotable about the longitudinal axis of a pan roller, certainly not about a pivot axis offset relative to this longitudinal axis. The applied pressure of the transfer roller against the pan roller and the thickness of the film layer conveyed through their roller nip can be set by the adjustment not of the pan roller, but of the transfer roller, along a slotted guide.
A further dampening unit is described in U.S. Pat. No. 5,540,145. That dampening unit is likewise an emulsion film dampening unit and is identical in many features to the just-described dampening unit.
A dampening unit described in Japanese published patent application JP SHO 51-92204 has an applicator roller which can be brought into frictional contact with the plate cylinder by a spring acting on a supporting lever. That dampening unit, however, lacks a pan roller and a transfer roller. The dampening unit comprises a metal roller which supplies the applicator roller with the dampening medium and which is in frictional contact with a body that absorbs dampening medium and the foot of which is dipped into a dampening medium container. The applicator is pivotable, together with the metal roller, about a supporting axis that is offset relative to the roller axis of the metal roller. The dampening medium quantity capable of being conveyed to the printing form by means of the absorbent body is comparatively small, so that that dampening unit is unsuitable for printing machines which print at high printing speeds.
German published patent application DE 29 49 594 A1 describes a dampening unit which has a pan roller, designated as a dampening duct roller, and a dampening applicator roller, but in which the dampening medium is transferred to the dampening applicator roller directly by the dampening duct roller, not via a transfer roller. Although the dampening applicator roller is pivotable about a pivot axis that is offset relative to the roller axis of the dampening duct roller, the dampening duct roller is not pivotable at all.
Furthermore, the prospectus xe2x80x9cPrinting Without Isopropanol (IPA)xe2x80x9d [xe2x80x9cDrucken ohne Isopropanol (IPA)xe2x80x9d] from the prospectus series xe2x80x9cGTO 52-Tipsxe2x80x9d issued by Heidelberger Druckmaschinen AG mentions a direct film dampening unit, for the operation and care of which instructions are given in the prospectus.
The object of the invention is to provide a further improved dampening unit for a planographic printing press which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this kind.
With the above and other objects in view there is provided, in accordance with the invention, a dampening unit of a planographic printing machine, such as a rotary offset printing machine, comprising:
a pan roller rotatably mounted about a pan roller axis;
a dampening unit roller;
a transfer roller disposed to be held in bearing contact against the dampening unit roller at a circumferential contact point with a regulating force;
the transfer roller and the pan roller being pivotably disposed about a pivot axis offset from the pan roller axis of the pan roller, the pivot axis lying substantially on a tangential line running through the circumferential contact point of the transfer roller and the dampening unit roller.
In accordance with an added feature of the invention, the regulating force is produced by a weight, a gas-pressure-generated force, and a spring force.
In accordance with an additional feature of the invention, the pan roller, the transfer roller, and the dampening unit roller are ink-friendly, emulsion-carrying rollers.
The dampening unit of a planographic printing machine, with a pan roller, a transfer roller and a dampening unit roller, the transfer roller being capable of being held in bearing contact against the dampening unit roller by means of a regulating force, in particular a weight, gas-pressure or spring force, is distinguished in that the transfer roller is pivotable, together with the pan roller, about a pivot axis offset relative to the roller axis of the pan roller and the pivot axis lies essentially on a tangential line running through a circumferential contact point which is formed by the transfer roller together with the dampening unit roller.
The fact that the common pivot axis of the transfer roller and of the dampening unit roller lies exactly or approximately on a common tangential line of the transfer roller and of the dampening unit roller, the tangential line running perpendicularly to the normal line along which the transfer roller is thrown onto the dampening unit roller, is highly advantageous in terms of a mounting which is free of any reaction to the pressure of the transfer roller against the dampening unit roller. If the circumferential contact point, through which the tangential line runs, is a slip-through nip formed by the transfer roller together with the dampening unit roller, the shear force taking effect in the slip-through nip during the shearing of the dampening-medium or emulsion film cannot exert any torque pivoting the transfer roller about the pivot axis. The force with which the transfer roller is thrown onto the dampening unit roller and which is generated by the regulating force therefore always remains constant, even in the event of variations in the shear force in the slip-through nip which are caused, for example, by a variation in the speed difference between the circumferential speeds of the transfer roller and of the dampening unit roller.
The fact that the pivot axis is offset relative to the roller axes of the pan roller and of the transfer roller makes it possible for the two rollers to be mounted in the same roller carrier, whilst the press-strip width in the nip of the two rollers can be adjustable by the displacement of the pan roller by an adjustment means. This is highly advantageous with regard to an accurately reproducible throw of the transfer roller onto the dampening unit roller, as also explained in detail at a later juncture.
As regards the design of the dampening unit as an emulsion or direct film dampening unit, each of the two measures, that is to say, on the one hand, the offset of the pivot axis and, on the other hand, the arrangement of the latter on or near the tangential line, is advantageous in itself and independently of the other in each case, and particular advantages arise from the combination of these measures.
In the dampening unit according to the invention, moreover, the pressure of the transfer roller against the dampening unit roller is advantageously self-regulating due to the regulating force. The width of the press strip formed by the transfer roller together with the dampening unit roller can be kept constant over the entire service life of these rollers by means of the force-accentuated throw of the transfer roller onto the dampening unit roller. This is a considerable advantage, as compared with an ex factory fixed setting of the rollers or as compared with a roller setting to be readjusted manually at regular intervals by the user.
In contrast to the prior art manufacturer-fixed setting of the rollers, in the dampening unit according to the invention variations in the diameter of the damping unit roller and/or of the transfer roller which occur as a consequence of use present no problems at all and are compensated by the action of the regulating force in the appropriate setting direction. The variations in diameter which are referred to may have various causes.
On the one hand, a circumferential rubber coating of the dampening unit roller may swell up due to the action of dampening medium or washing medium, with the result that the diameter of the dampening unit roller increases.
On the other hand, such a soft-elastic dampening unit roller, by rolling on the transfer roller, may experience wear. If, during the operation of the dampening unit, the dampening unit roller and the transfer roller roll on one another at mutually different circumferential speeds, even greater abrasion of the dampening unit roller may occur. The diameter of the dampening unit roller decreases due to wear and abrasion.
As a rule, the two effects are superposed, for example, in a first stage, the swelling up of the dampening unit roller and, in a subsequent second stage, the abrasion of the dampening unit roller being the predominant effect, so that the diameter of the dampening unit roller fluctuates over its service life.
In the highly maintenance-friendly dampening unit according to the invention, there is no need for any check of the press-strip width or for any manual readjustment of the dampening unit roller and transfer roller over the service life of the dampening unit roller.
In order to adapt the pressure of the transfer roller against the dampening unit roller to different printing conditions, the magnitude of the regulating force may, of course, be adjustable. If the regulating force acting on the transfer roller is, for example, a spring force applied by a spring, the spring force taking effect during pressing may be adjustable by means of a variation in the prestress of the spring.
Preferably, the transfer roller is held solely by the action of the regulating force during the dampening of the printing form on the rotating dampening unit roller and is therefore not additionally fixed.
However, the scope of the invention also includes a design variant, in which the transfer and dampening unit rollers are stationary or rotate at the same circumferential speed, so that no shear forces take effect in the roller nip formed by the two rollers, when the transfer roller is thrown against the dampening unit roller with a pressing pressure determined by the regulating force, for example in a sprung manner. The relative position, set by means of the regulating force, of the transfer roller in relation to the dampening unit roller can thereafter be secured by means of an additional fixing device, for example a clamping device, so that, when a roller rotation drive is subsequently switched on or changed over, for dampening the printing form, to roller rotation at different circumferential speeds or rolling slip, the fixed pressing pressure is maintained. In this design variant, variations in the diameter of the two rollers are compensated, even before fixing, by means of the regulating forcexe2x80x94here a compensating force.
In accordance with another feature of the invention, which is advantageous in terms of as small a number of gaps as possible in the transport path of the dampening medium from the dampening medium container to a printing form, the dampening unit roller is a dampening applicator roller which can be set selectively in bearing contact against the printing form or at a distance from the printing form. In specific applications, however, the dampening unit roller may, in contrast, also be a further transfer roller which transfers the dampening medium from the first-mentioned transfer roller onto a dampening applicator roller.
In accordance with a further feature of the invention, which is likewise advantageous in terms of as small a number of gaps as possible in the transport path of the dampening medium, the transfer roller is a metering roller which is in rolling contact with the pan roller. In this embodiment, the transfer roller thus has a double function, in that the transfer roller, on the one hand, transfers the dampening medium taken over from the pan roller onto the dampening unit roller and, on the other hand, together with the pan roller, forms a roller nip of adjustable size for producing the dampening medium film and for metering the dampening medium.
In an embodiment which is advantageous in terms of a displacement of the transfer roller into a washing position separated from the dampening unit roller, the transfer roller is capable, by means of a roller setting drive, of being displaced at a distance from the dampening unit roller counter to the resilient return effect of the regulating force.
In an embodiment which is advantageous in terms of the design of the dampening unit as a direct film dampening unit, the transfer roller is driven by a roller rotation drive at a circumferential speed differing from the circumferential speed of the dampening unit roller.
In this context, the possibility, already referred to, that the transfer roller forms, with the two rollers adjacent to it, two different roller nips, each performing a special function, is particularly favorable.
In the slip-through nip formed by the transfer roller together with a dampening unit roller, faults in the dampening medium film located on the dampening unit roller, which originate from the printing image of the printing form, are blurred in the circumferential direction, the transfer roller preferably rotating more slowly than the dampening unit roller.
The roller nip formed by the transfer roller together with the pan roller serves, as already mentioned, for producing a film, and the transfer roller functioning as a metering roller can roll without rolling slip on the pan roller.
The small number of only three rollers in the roller train transporting the dampening medium from the dampening medium container to the printing form is advantageous, particularly when the dampening unit is designed as a direct film dampening unit, a highly stable printing ink/dampening medium emulsion being ensured if an alcohol-free dampening medium or alcohol-substitutes in the dampening medium are used.
In accordance with again a further embodiment which is likewise advantageous in terms of a design of the dampening unit as a direct film dampening unit, the transfer roller is driven by a roller rotation drive at a circumferential speed that differs from the circumferential speed of the rotating printing form dampened by the dampening unit. In a preferred embodiment, the transfer roller rotates substantially more slowly, that is to say at a lower circumferential speed, than the printing form.
In an embodiment which is advantageous in terms of the prevention or at least the sufficient reduction of fluctuations in the normal force between the transfer roller and the dampening unit roller during printing, said fluctuations being caused, for example, by deformed or nonround rollers, the common pivot axis of the transfer roller and of the pan roller is designed as a rotary bearing which is rotatable smoothly in a first direction of rotation and sluggishly in a second direction of rotation, so that the transfer roller is capable of being pivoted about the rotary bearing against the dampening unit roller smoothly and away from the dampening unit roller sluggishly. This special design of the pivot axis ensures an accurately reproducible movement of throwing the transfer roller onto the dampening unit roller and, at the same time, a damping of the movement of throwing the transfer roller off the dampening unit roller.
The rotary bearing described below constitutes, on the one hand, an advantageous development of the rotary bearing of the last-described embodiment of the dampening unit according to the invention and, on the other hand, an autonomous invention independent of the dampening unit.
The rotary bearing on a machine processing a print carrier, in particular on a printing machine, in particular as the dampening unit rotary bearing forming the pivot axis, is distinguished either in that a freewheel coupling, inherently smoothly rotatable, is slidably mounted, so as to be sluggishly rotatable, in a joint bore and a joint pin is inserted fixedly in terms of rotation into the freewheel coupling (first variant) or in that a freewheel coupling, inherently smoothly rotatable, is slidably mounted, so as to be sluggishly rotatable, on a joint pin and is inserted fixedly in terms of rotation into a joint bore (second variant).
It is specific to the two alternative variants of the rotary bearing that a machine part, for example a roller carrier carrying the pan roller and the transfer roller of the dampening unit, said machine part being mounted in the rotary bearing, is rotatable or pivotable about the rotary bearing smoothly in a first direction of rotation and sluggishly in a second direction of rotation.
During the rotation of the machine part in the first direction of rotation, an inherent rotation of the freewheel coupling in its freewheeling rotation direction takes place. In this case, there is no or at least no appreciable rotation within the sliding bearing which is formed, in the first variant, by the freewheel coupling or its outer ring together with the joint bore and which is formed, in the second variant, by the freewheel coupling or its inner ring together with a joint pin.
During the rotation of the machine part in the opposite second direction of rotation, an inherent rotation of the freewheel coupling is blocked or the return of the freewheel coupling is blocked, so that there is only rotation in the sliding bearing formed by the freewheel coupling together with the joint bore or together with the joint pin.
Freewheel couplings per se are machine elements which are often used in mechanical engineering. Reference may nevertheless be made, at this juncture, to the manual xe2x80x9cKonstruktionselemente der Feinmechanikxe2x80x9d [xe2x80x9cConstruction Elements in Precision Mechanicsxe2x80x9d] (ISBN 3-446-15332-2), published by Carl Hanser Verlag Munich, Vienna 1989, Werner Krause (ed.), and, in particular, to pages 512-13 thereof. It can be gleaned, inter alia, from the manual that freewheel couplings can be divided into couplings dependent on the direction of rotation and having a positively acting directional locking mechanism and couplings dependent on the direction of rotation and having a frictionally acting directional locking mechanism. The freewheel couplings with a positively acting directional locking mechanism include freewheel couplings with a toothed directional locking mechanism which are used, for example, for ratchets and preferably movements with very low rotational speeds. For higher rotational speeds, it is preferable to use low-noise freewheel couplings with a frictionally acting directional locking mechanism which are designed, for example, as clamping-roller or clamping-body freewheels and can be delivered and used as so-called built-in freewheels, such as ball bearings.
Such a built-in freewheel is preferably used to produce the rotary bearing forming the pivot axis of the dampening unit.
In the first variant of the rotary bearing according to the invention, with a joint pin inserted fixedly in terms of rotation into the freewheel coupling, the joint pin is fastened, so as to be secured against rotation, to a further machine part. In the second embodiment with a freewheel coupling inserted fixedly in terms of rotation into the joint bore, the machine part having the joint bore is fastened, so as to be secured against rotation, to a further machine part. When the freewheel coupling is used according to the invention in order to produce the rotary bearing, there is no rotational movement transmitted to the joint pin by the machine part having the joint bore and there is also no rotational movement transmitted from the joint pin to the machine part having the pivot joint bore.
In the two variants of the rotary bearing which are described, its sluggishly moving sliding bearing may be designed so as to include a bearing bush. The advantage of using a bush is its good cutting machinability, so that the diameter fit dimension necessary for the sluggishness of the sliding bearing can be produced, for example, completely without any cutting machining of the freewheel coupling. The use of a bush to form the sliding bearing is also advantageous because the bush can function as the softer wearing part of the sliding bearing and be manufactured cost-effectively as a replacement part. Wear of the freewheel, the outer ring and/or the inner ring of which may be hardened, said wear being caused by the friction within the sliding bearing, is thus minimized.
In the first variant, the bush can be inserted fixedly in terms of rotation into a machine part, the inner wall of the bush forming the joint bore, in which an outer ring of the freewheel coupling is rotatable with comparatively high friction. The bush may, however, also be slipped fixedly in terms of rotation onto the outer ring of the freewheel coupling and, for example, shrunk on, so that the bush becomes virtually an integral part of the freewheel coupling. In this case, the outer face of the bush, together with the joint bore located in a machine part, forms the sluggish sliding bearing.
In the second variant of the rotary bearing with the freewheel coupling slidably mounted, so as to be sluggishly rotatable, on the joint pin, it is likewise possible, in a similar way, for the freewheel coupling to be seated on a bush and for this bush to be seated on the joint pin. If, for example, the inner ring of the freewheel coupling is seated, so as to be secured against rotation, on the outer face of that bush, the inner face of the bush, together with the joint pin, then forms the sluggish sliding bearing. The bush may, however, also be seated on the joint pin so as to be secured against rotation relative to the latter, the outer face of the bush, together with the inner ring of the freewheel coupling, forming the sluggish sliding bearing.
The freewheel coupling inner ring, mentioned many times in the above explanations, is often also designated as an inner star in the case of clamping-roller freewheels and as a clamping-body ring in the case of freewheel couplings with clamping bodies connected to form a ring.
The rotary bearing according to the invention is suitable for mounting any pivotable machine part which is to be pivotable in one pivoting direction with low friction and in the other pivoting direction with increased friction and therefore sluggishly. The rotary bearing may thus act as a rotational and directionally dependent shock absorber.
In accordance with another feature of the invention, the rotary bearing having a pivot axis includes a smoothly rotatable freewheel coupling slidably mounted, so as to be sluggishly rotatable, on a joint pin, and non-rotatably fixed in a pivot joint bore of a machine frame.
In accordance with another feature of the invention, the rotary bearing having a pivot axis includes a smoothly rotable freewhel coupling slidably mounted, so as to be sluggishly rotable, on a joint pin, and non-rotatably fixed in a pivot joint bore of a machine frame.
In an embodiment of the dampening unit according to the invention which is advantageous in terms of the metering of the dampening medium quantity, the transfer roller and the pan roller are mounted together in a roller carrier with an adjustable roller center distance between them. For example, by the transfer roller being displaced relative to the pan roller, the pressing of the transfer roller against the pan roller and consequently the dampening medium quantity conveyed through the roller nip formed by the two rollers pressed one onto the other can be set. In order to set the roller center distance, a setting device may be arranged on the roller carrier.
In an embodiment which is advantageous in terms of a high reproducibility of the throw of the transfer roller onto the dampening unit roller, the roller center distance between the axis of rotation of the pan roller and the axis of rotation of the transfer roller can be set, by means of an adjusting device formed on the roller carrier, by the displacement of the pan roller selectively in the direction toward the transfer roller or in the direction away from the transfer roller. Consequently, it is no longer necessary to displace the transfer roller in order to set the roller pressure, and the transfer roller can be mounted rotatably in the roller carrier in a fixed position relative to the latter. This ensures that, during the pivoting of the roller carrier about the pivot axis or about the rotary bearing which forms the latter, the transfer roller always comes to bear against the dampening unit roller at absolutely the same circumferential point on the latter. A constant distance of the transfer roller from a point of action of the regulating force on the roller carrier and a constant distance of the transfer roller from the pivot axis are also ensured, so as to rule out a variation in the pressing force of the transfer roller against the dampening unit roller, said variation being caused by any variations in these distances.
In an embodiment which is advantageous in terms of the cleaning of the pan roller, the pan roller can be brought into bearing contact against a distributor roller traversing in its axial direction. A washing fluid can thus be transferred from the distributor roller onto the pan roller, and, during the cleaning of the dampening unit, dirt located on the pan roller can be taken off by the distributor roller. In this case, the pan roller and/or the distributor roller preferably has a soft coating. For example, the pan roller is provided with a soft rubber layer on the circumference.
If the distributor roller is shorter than the pan roller, as seen in the axial direction, the circumferential end regions of the pan roller, which per se, with the distributor roller being in the middle position relative to the pan roller, project beyond the distributor roller in the axial direction, are also covered, during cleaning, as a result of the oscillation of the distributor roller, so that the pan roller is cleaned over its entire length via the distributor roller. The transfer roller may likewise be longer than the distributor roller and, for example, be of the same length as the pan roller and is also cleaned via the pan roller by being in bearing contact against the latter.
The throwing of the pan roller onto the distributor roller may be brought about by a pivoting of the roller carrier carrying the pan roller about the pivot bearing.
In an embodiment which is advantageous in terms of the cleaning of the transfer roller, the transfer roller can be brought into bearing contact against an axially traversing distributor roller. The distributor roller rolling on the transfer roller can thus transfer a washing fluid onto the transfer roller and take off dirt, for example printing ink residues, from the latter. In order to throw the transfer roller onto the distributor roller, the roller carrier carrying the transfer roller may be pivotable about the rotary bearing, in which the roller carrier is mounted rotatably and which forms the pivot axis.
If the distributor roller in this embodiment is shorter than the transfer roller, as seen in the axial direction, during the cleaning of the transfer roller the oscillation of the distributor roller results, in principle, in the same advantages as those afforded in the cleaning of the pan roller via the distributor roller, said cleaning already being mentioned in connection with the preceding embodiment. The roller ends of the transfer roller which project beyond the distributor roller are covered by the oscillation of the distributor roller, so that the transfer roller is cleaned over its entire length via the distributor roller. In this case, the pan roller may be longer than the distributor roller and, for example, be exactly as long as the transfer roller and also be cleaned via the latter, the pan roller bearing against the transfer roller.
The pan roller and the transfer roller, which is designed as a metering roller, should be axially longer than the dampening unit roller, designed, in particular, as a dampening applicator roller, so that the transfer of so-called lateral water margins into the region of the printing image is avoided.
When dampening units are in operation, such water margins are often formed, due to the interaction of the pan roller and metering roller, on those circumferential regions of the pan roller and metering roller which are located at both ends and are near the roller edges. The watery circumferential strips may, as measured from the respective side edge of the roller, extend about 1 centimeter in the direction of the other roller end. Since the water margins are formed on circumferential regions projecting beyond the dampening unit roller in the axial direction, this water excess is not transferred onto the dampening unit roller and not from the latter onto the printing form. Thus, since the pan roller and metering roller are designed to be somewhat longer than the dampening unit roller, this affords a technical solution avoiding water margin effects which impair the print quality.
In a possible design of the dampening unit according to the invention as an alcohol dampening unit, in which the pan roller and the transfer roller do not carry ink, the technical solution found does not present any other problems.
In the preferred design of the dampening unit according to the invention as a direct film dampening unit, the pan roller and the transfer roller are ink-carrying and, for this purpose, are each provided, for example, with a circumferential hard or soft rubber layer. Where the direct film dampening unit is concerned, it is therefore necessary, in contrast to the alcohol dampening unit, for the pan roller and the transfer roller also to be capable of being cleaned. In order to clean the pan roller and the transfer roller, which is designed as a metering roller, the washing fluid must be supplied to the pan roller or the transfer roller via a further roller which, for this purpose, rolls on the pan roller or on the transfer roller during cleaning.
For example, in a first cleaning variant, the washing fluid is transferred from the further roller to the transfer roller and from the transfer roller onto the pan roller. In this case, the further roller serves for transporting away, in the opposite direction to the supply of washing fluid, the printing ink residues to be removed from the pan roller and the transfer roller during cleaning. In this case, the transfer roller and/or the further roller (distributor roller) preferably has a soft coating. It is also possible, according to a second cleaning variant, for the printing ink residues located on the transfer roller to be taken off from the pan roller and for the printing ink residues located on the pan roller to be taken off from the further roller rolling on the pan roller during cleaning, that is to say the transfer roller is co-washed via the pan roller. The pan roller and/or the further roller (distributor roller) in this case preferably have a soft coating.
In both cleaning variants, it is beneficial if the further roller is designed as a distributor roller which traverses axially during cleaning and the stroke width of which is dimensioned such that, during cleaning, the distributor roller also covers those circumferential regions of the pan roller or metering roller which are on both sides and on which the dirty water margins or emulsion margins are located. It is also beneficial if the lateral stroke width is dimensioned such that both the left side edge and the right side edge of the distributor roller terminates a little way beyond the corresponding side edge of the respective roller, that is to say the pan roller or the transfer roller, onto which the distributor roller is thrown during cleaning.
In an embodiment which is advantageous in terms of designing the dampening unit so as to be capable of being set with a particularly high degree of metering accuracy, at least two rollers roll on the pan roller, one roller of which can be set selectively in bearing contact against an axially traversing distributor roller or at a distance from the distributor roller. Preferably, the two rollers are formed by the transfer roller and a squeezing roller, and, as seen in the direction of rotation of the pan roller, the squeezing roller follows the pan roller circumferential region dipping into the stored dampening medium and precedes the bearing point of the transfer roller against the pan roller. The squeezing roller is, in this case, that roller which, for example for cleaning purposes, is capable of being thrown onto the distributor roller.
On grounds of avoiding lateral water margins on the squeezing roller, which have an adverse effect in the printing region, the axial length of the squeezing roller may be somewhat longer than that of the distributor roller and be dimensioned so as to be the same length as the pan roller and the transfer roller, in which case, in a similar way to the embodiments already described above, the circumferential end regions of the squeezing roller, which, with the distributor roller in the middle position, project beyond the side edges of the distributor roller, are also covered as a result of the oscillation of the distributor roller while the squeezing roller is being cleaned via said distributor roller. The cleaning of the squeezing roller and, via the latter, the cleaning of the pan roller and of the transfer roller bearing against the pan roller, is carried out, in the way described in connection with the two preceding embodiments, by means of a cleaning device assigned to the inking unit which, during cleaning, is connected to the dampening unit via a roller train.
In accordance with again an added feature of the invention, which is advantageous in terms of the smoothing of the dampening medium and, if the dampening unit is designed as a direct film dampening unit, in terms of the formation of an emulsion and the smoothing of the emulsion before application to the printing form, the distributor roller is in rolling contact with the dampening unit roller during dampening. For example, the distributor roller may be in permanent bearing contact against the dampening unit roller designed as a dampening applicator roller.
In accordance with again an additional feature of the invention, which is advantageous in terms of the bearing of the transfer roller against the dampening unit roller in a way unimpaired by drive influences, the roller rotation drive driving the transfer roller is pivotable, together with the transfer roller, about the pivot axis offset relative to the roller axis of the pan roller. For example, the roller rotation drive is an electric motor and is fastened to the roller carrier carrying the transfer roller and pivotable about the pivot axis. It is thus possible to transmit the drive forces, generated by the roller rotation drive, for driving the transfer roller and for generating the rolling slip of the transfer roller relative to the dampening unit roller from the roller rotation drive to the transfer roller, in such as way as to avoid a torque which is exerted on the roller carrier by the drive forces, pivots the roller carrier about the pivot axis and is in the same direction as or opposite to the action of the regulating force on the roller carrier.
In many cases, it may be necessary to have an electric motor arrangement which differs from this embodiment and is external to the roller carrier, the drive forces being transmitted from the electric motor to the transfer roller via a gear comprising, for example, a toothed belt or gearwheels. In these cases, it is advantageous to arrange the gear in such a way that the line of action of the drive force, which corresponds, for example, to the belt run, runs through the pivot axis or at least near to the pivot axis. In this way, even when the electric motor is arranged externally to the roller carrier, drive-induced torques having a disturbing effect on the bearing of the transfer roller against the dampening unit roller and exerted on the roller carrier are avoided.
The dampening unit according to the invention and its embodiments are suitable particularly for offset rotary printing machines and may also be employed for dampening the planographic printing form on printing machines which print by direct planographic printing (direct lithography) without rubber blanket cylinders.
In accordance with a preferred embodiment of the invention, the dampening unit is designed as an emulsion film or direct film dampening unit, by means of which a high print quality is achieved without the use of alcohol or alcohol substitutes, which requires no cooling since it is highly operator-friendly, and by means of which shorter drying times for the printed sheets and a more favorable proving behavior with fewer starting discards, as compared with alcohol dampening units.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a dampening unit of a planographic printing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however; together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.